Light emitting device

ABSTRACT

A light emitting device is provided that includes a substrate, a light emitting unit formed on the substrate, and an encapsulation unit. The encapsulation unit may include a first region corresponding to the light emitting unit and a second region coalesced with the substrate. The encapsulation unit of the first region or a part of the encapsulation unit of the first region may have a positive curvature.

The present application is a Divisional Application of U.S. patentapplication Ser. No. 11/987,754, filed Dec. 4, 2007, now U.S. Pat. No.7,723,747 which claims priority from Korean Patent Application No.10-2007-0021091, filed Mar. 2, 2007, the subject matters of which areincorporated herein by reference. The present application claimspriority under 35 U.S.C. §120 from U.S. patent application Ser. No.11/987,754.

BACKGROUND

1. Field

Embodiments of the present invention may relate to displays. Moreparticularly, embodiments of the present invention may relate to a lightemitting device.

2. Background

A light emitting device is a self-light emitting device having a lowdriving voltage and a high emission efficiency that can emit a varietyof colors. The light emitting device may be made thin and may havepatterns easily formed therein. The light emitting device is a type offlat display device.

The light emitting device may include two electrodes and a lightemitting unit having a light emitting layer formed between the twoelectrodes.

The light emitting device may experience degradation due to moisture,oxygen, ultraviolet rays and so on. The degradation may include externalforces applied to the device in a fabrication process of the device orduring use.

External moisture and oxygen may oxidize a light emitting unit thatincludes an organic material, and thus may degrade and damage the lightemitting unit. Thus, moisture and oxygen may have a detrimental effecton lifespan of the light emitting device. Accordingly, a sealingstructure for encapsulating the light emitting unit may be used. Theencapsulation unit or an encapsulation substrate formed of metal, glass,plastic or the like may be connected to a lower substrate using asealing material, such as a sealant, in order to encapsulate theinternal elements.

If external pressure is applied, the light emitting unit may experiencedegradation and damage due to contact of the light emitting unit and theencapsulation unit or contact of the light emitting unit and a getter.

If the light emitting device is used for a long period of time, athickness of the getter that absorbs moisture may become thick. Thus,the getter and the light emitting unit may be brought in contact witheach other, thereby causing partial degradation and/or damage to thelight emitting unit.

If the size of the getter is decreased in order to prevent the problem,the light emitting device may not provide sufficient moistureabsorption. Further, if the space between the light emitting unit andthe getter is too large, then an overall thickness of the light emittingdevice may become too thick.

BRIEF DESCRIPTION OF THE DRAWINGS

Arrangements and embodiments may be described in detail with referenceto the following drawings in which like reference numerals refer to likeelements and wherein:

FIGS. 1A to 1C illustrate various implementations of a color imagedisplay method in an organic light emitting device;

FIGS. 2A to 2C are plan and cross-sectional views illustrating a lightemitting device in accordance with example embodiments of the presentinvention;

FIGS. 3A to 3C are plan and cross-sectional views illustrating a lightemitting device in accordance with example embodiments of the presentinvention; and

FIGS. 4A to 4C are plan and cross-sectional views illustrating a lightemitting device in accordance with example embodiments of the presentinvention.

DETAILED DESCRIPTION

FIGS. 1A to 1C illustrate various implementations of a color imagedisplay method in an organic light emitting device. Otherimplementations may also be used. FIG. 1A illustrates a color imagedisplay method in an organic light emitting device that separatelyincludes a red organic emitting layer 15R to emit red light, a greenorganic emitting layer 15G to emit green light and a blue organicemitting layer 15B to emit blue light. The red, green and blue lightproduced by the red, green and blue organic emitting layers 15R, 15G and15B may be mixed to display a color image.

In FIG. 1A, the red, green and blue organic emitting layers 15R, 15G and15B may each include an electron transporting layer, an emitting layer,a hole transporting layer, and the like. FIG. 1A also shows a substrate10, an anode electrode 12 and a cathode electrode 18. Differentdispositions and configurations of the substrate 10, the anode electrode12 and the cathode electrode 18 may also be used.

FIG. 1B illustrates a color image display method in an organic lightemitting device that includes a white organic emitting layer 25W to emitwhite light, a red color filter 20R, a green color filter 20G and a bluecolor filter 20B.

As shown in FIG. 1B, the red color filter 20R, the green color filter20G and the blue color filter 20B each receive white light produced bythe white organic emitting layer 25W and produce red light, green lightand blue light, respectively. The red, green and blue light may be mixedto display a color image. And an organic light emitting device mayfurther include a white color filter. So the organic light emittingdevice may realization various colors by manner of R/G/B or R/G/B/W.

In FIG. 1B, the white organic emitting layer 25W may include an electrontransporting layer, an emitting layer, a hole transporting layer, andthe like.

FIG. 1C illustrates a color image display method in an organic lightemitting device that includes a blue organic emitting layer 35B to emitblue light, a red color change medium 30R, a green color change medium30G and a blue color change medium 30B.

As shown in FIG. 1C, the red color change medium 30R, the green colorchange medium 30G and a blue color change medium 30B each receive bluelight produced by the blue organic emitting layer 35B and produce redlight, green light and blue light, respectively. The red, green and bluelight may be mixed to display a color image. In FIG. 1C, the blueorganic emitting layer 35B may include an electron transporting layer,an emitting layer, a hole transporting layer, and the like.

Embodiments of the present invention may provide a light emitting deviceto prevent degradation and damage of a light emitting unit due tocontact with an encapsulation unit or a getter, for example.

Embodiments of the present invention may provide a light emitting devicethat includes a substrate, a light emitting unit formed on thesubstrate, and an encapsulation unit having a first region correspondingto the light emitting unit and a second region to couple with thesubstrate (via a sealant). The encapsulation unit at the first region ora part of the encapsulation unit at the first region may have a positivecurvature that projects away from the substrate.

The light emitting device may perform top emission or bottom emission.Embodiments of the present invention may be applicable to activedisplays and passive displays. Although passive devices are describedfor ease of convenience, embodiments of the present invention may alsobe provided with respect to an active device that includes a thin filmtransistor (TFT). The thin film transistor may have a semiconductorlayer, a gate electrode, a source electrode and a drain electrode on thesubstrate.

FIGS. 2A to 2C are plan and cross-sectional views illustrating a lightemitting device in accordance with example embodiments of the presentinvention. Other embodiments and configurations are also within thescope of the present invention. The cross sections of FIGS. 2B and 2Care views taken along line C1-C2 of the plan view shown in FIG. 2A.

As shown in FIGS. 2A to 2C, a light emitting device 100 may include asubstrate 110, a light emitting unit 120, an encapsulation unit 160 anda getter 150. The substrate 110 may be formed from glass, metal, plasticor the like.

The light emitting unit 120 may be formed on the substrate 110. Thelight emitting unit 120 may include a first electrode 122, a lightemitting layer 124 and a second electrode 126. The light emitting layer124 including an organic or an inorganic material may be formed over thefirst electrode 122. The second electrode 126 may be formed on the lightemitting layer 124 in such a way to cross the first electrode 122.

A thin film transistor (not shown) having a semiconductor layer, asource electrode, a drain electrode and a gate electrode may also beprovided over the substrate 110. The source electrode or the drainelectrode of the thin film transistor may be electrically connected tothe first electrode 122.

The first electrode 122 may serve as an anode electrode for injectingholes into the light emitting layer 124. The first electrode 122 may beformed of a transparent material having a high work function such asindium tin oxide (ITO) or indium zinc oxide (IZO).

The second electrode 126 may serve as a cathode electrode for injectingelectrons into the light emitting layer 124. The second electrode 126may be formed using aluminum, silver, magnesium and/or an alloy thereof.

The material to form the second electrodes and/or a thickness thereofmay vary depending on various factors including size, a light emittingstructure, an active or passive type, etc. of the light emitting device.

The encapsulation unit 160 may be formed over the substrate 110 on whichthe light emitting unit 120 is formed. The encapsulation unit 160 canencapsulate the light emitting unit 120 and the substrate 110 in whichvarious elements are formed. The encapsulation unit 160 may be formedusing glass, plastic and/or metal. Other materials may also be used.

The encapsulation unit 160 may include a first region X corresponding tothe light emitting unit 120 and a second region Y that aligns with thesubstrate 110. The second region Y of the encapsulation unit 160 may bealigned with an edge of the substrate 110 using a sealing material, suchas a sealant 180 or frit. The second region Y may be a region of theencapsulation unit 160 that couples to the substrate 110 via the sealant180. The second region Y may also be considered outside the first regionX.

The getter 150 may be formed under the first region X of theencapsulation unit 160. The getter 150 may remove oxygen, moisture,etc., that are generated within the device or are externallyinfiltrated.

A surface having a curvature may have a better durability than a flatsurface against deformation due to external force. Therefore, the firstregion X of the encapsulation unit 160 may have a positive curvaturethat upwardly projects from the substrate 110 (or projects away from thesubstrate 110). The first region X of the encapsulation unit 160 mayhave a concave down shape as shown in FIG. 2A.

If the first region X of the encapsulation unit 160 has a positivecurvature with a top point that is far from the substrate 110, then aspace between the light emitting unit 120 and the getter 150 may beprovided. Although the getter 150 may become thick through absorption ofmoisture or oxygen, the possibility of contact of the light emittingunit 120 and the getter 150 may decrease due to the increased space.

If the space between the light emitting unit 120 and the getter 150 isincreased, then a plurality of getters may be provided. The device maythereby be protected more effectively from moisture and water.

The encapsulation unit 160 may include an upper surface 160 a and alower surface 160 b at the first region X. The lower surface 160 b maybe a surface that faces the substrate 110, and the upper surface 160 amay be a surface that faces away from the substrate 110. Both the uppersurface 160 a and the lower surface 160 b may have a positive curvaturesuch as shown in FIG. 2A. The upper surface 160 a and the lower surface160 b may both have a same shape (i.e., a curved shape) such as shown inFIG. 2A.

The lower surface 160 b may have a positive curvature and the uppersurface 160 a may be flat and parallel to the substrate 110 such asshown in FIGS. 2B and 2C.

The encapsulation unit 160 may also include an upper surface 160 c and alower surface 160 d at the second region Y. The lower surface 160 d maybe a surface that faces the substrate 110, and the upper surface 160 cmay be a surface that faces away from the substrate 110. The uppersurface 160 a at the first region X and the upper surface 160 c at thesecond region Y may both be separately flat and parallel to thesubstrate 110 such as shown in FIGS. 2B and 2C. The upper surface 160 aof the encapsulation unit 160 at the first region X and the uppersurface 160 c of the encapsulation unit 160 at the second region Y maybe formed along a common plane such as shown in FIG. 2C.

A height d may be a distance between a first plane defined by the lowersurface 160 d of the encapsulation unit 160 at the second region Y and asecond plane (parallel to the first plane) defined by a top point of thelower surface 160 b of the encapsulation unit 160 at the first region X.The top point may be a point of the lower surface 160 b that is furthestfrom the substrate 110 (or the light emitting unit 120). The height dmay range from 10 μm to 100 μm, for example. If the height d is 10 μm ormore, degradation of picture quality caused by an interferencephenomenon between light emitted from the light emitting device 100 tothe encapsulation unit 160 and light incident to the encapsulation unit160 from outside may be reduced. If the height d is 100 μm or less,thickness of the device may be prevented from becoming too thick.

Stated differently, the encapsulation unit 160 may include a firstsurface (i.e., the lower surface 160 b) at the first region X that facesthe substrate 110 and a second surface (i.e., the lower surface 160 d)at the second region Y that faces the substrate 110, where the firstsurface includes a top point that is furthest from the substrate 110.The second surface may define a first plane and the top point may be ona second plane that is parallel to the first plane. A distance betweenthe first plane and the second plane may be within a range of 10 μm to100 μm.

FIGS. 3A to 3C are plan and cross-sectional views illustrating a lightemitting device in accordance with example embodiments of the presentinvention. The cross sections of FIGS. 3B and 3C are views taken alongline C1-C2 of the plan view shown in FIG. 3A. Other embodiments andconfigurations are also within the scope of the present invention.

As shown in FIGS. 3A to 3C, an encapsulation unit 260 of a lightemitting device 200 may include the first region X corresponding to thelight emitting unit 120 and the second region Y that aligns with thesubstrate 110. At least one part of the first region X of theencapsulation unit 260 may have a positive curvature that upwardlyprojects from the substrate 110 (or projects away from the substrate110). That is, the first region X of the encapsulation unit 260 may havea concave down shape (with respect to the substrate 110), such as shownin FIGS. 3A-3C.

The first region X of the encapsulation unit 260 may include a centralarea A having a positive curvature and an edge area B having a crosssection surface with a flat shape or a straight-line shape (and withouthaving a curvature or any substantial curvature). The edge area B may beprovided about the central area A such that the edge area B is adjacent(or about) the second region Y.

A surface having a curvature may have better durability than a flatsurface against deformation due to external force. Therefore, thecentral area A may have a positive curvature that upwardly projects fromthe substrate 110 (or projects away from the substrate 110).

If the first region X of the encapsulation unit 260 has a positivecurvature with a top point that is far above the substrate 110, then aspace between a light emitting unit 120 and the getter 150 may beprovided. Although the getter 150 may become thick through absorption ofmoisture or oxygen, the possibility of contact of the light emittingunit 120 and the getter 150 may decrease due to the increased space.

If the space between the light emitting unit 120 and the getter 150 isincreased, then a plurality of getters may be provided. The device maythereby be protected more effectively from moisture and water.

The edge area B (of the first region X) may have a cross section surfacewith a flat shape or a straight-line shape. The edge area B (of thefirst region X) may extend from (or be defined by) an inner edge (orend) of the second region Y to a region aligned with one end of thelight emitting unit 120 formed on the substrate 110 such as shown inFIG. 3A.

The encapsulation unit 260 may include an upper surface 260 a and alower surface 260 b at the first region X. The lower surface 260 b maybe a surface that faces the substrate 110, and the upper surface 260 amay be a surface that faces away from the substrate 110. Both the uppersurface 260 a and the lower surface 260 b at the central area A may havea positive curvature such as shown in FIG. 3A. The upper surface 260 aand the lower surface 260 b may both have a same shape (i.e., a curvedshape) such as shown in FIG. 3A.

Further, the upper surface 260 a and the lower surface 260 b at the edgearea B may have a flat shape or a straight-line shape such as shown inFIG. 3A. That is, the upper surface 260 a and the lower surface 260 b atthe edge area B may both have a same shape such as shown in FIG. 3A.

The upper surface 260 a at the first region X may have a flat shape thatis parallel to the substrate 110 (regardless of the lower surface 260 b)such as shown in FIGS. 3B-3C.

The encapsulation unit 260 may also include an upper surface 260 c and alower surface 260 d at the second region Y. The lower surface 260 d maybe a surface that faces the substrate 110, and the upper surface 260 cmay be a surface that faces away from the substrate 110. The uppersurface 260 a at the first region X and the upper surface 260 c at thesecond region Y may both be separately flat and parallel to thesubstrate 110 such as shown in FIGS. 3B-3C. The upper surface 260 a ofthe encapsulation unit 260 at the first region X and the upper surface260 c of the encapsulation unit 260 at the second region Y may be formedalong a common plane such as shown in FIG. 3C.

A height d may be a distance between a first plane defined by the lowersurface 260 d of the encapsulation unit 260 at the second region Y and asecond plane (parallel to the first plane) defined by a top point of thelower surface 260 b of the encapsulation unit 260 at the first region X.The top point may be a point of the lower surface 260 b that is furthestfrom the substrate 110 (or the light emitting unit 120). The height dmay range from 10 μm to 100 μm. If the height d is 10 μm or more,degradation of picture quality caused by an interference phenomenonbetween light emitted from the light emitting device 200 to theencapsulation unit 260 and light incident to the encapsulation unit 260from outside may be reduced. If the height d is 100 μm or less,thickness of the device may be prevented from becoming too thick.

Stated differently, the encapsulation unit 260 may include a firstsurface (i.e., the lower surface 260 b) at the first region X that facesthe substrate 110 and a second surface (i.e., the lower surface 260 d)at the second region Y that faces the substrate 110, where the firstsurface includes a top point that is furthest from the substrate 110.The second surface may define a first plane and the top point may be ona second plane that is parallel to the first plane. A distance betweenthe first plane and the second plane may be within a range of 10 μm to100 μm.

FIGS. 4A to 4C are plan and cross-sectional views illustrating a lightemitting device in accordance with example embodiments of the presentinvention. Other embodiments and configurations are also within thescope of the present invention.

As shown in FIGS. 4A to 4C, an encapsulation unit 360 of a lightemitting device 300 may include the first region X corresponding to thelight emitting unit 120 and a second region Y that aligns with thesubstrate 110. At least one part of the first region X of theencapsulation unit 260 may have a positive curvature that upwardlyprojects from the substrate 110 (or projects away from the substrate110).

The first region X of the encapsulation unit 360 may include the centralarea A and the edge area B. The edge area B may have a positivecurvature that upwardly projects from the substrate 110 (or projectsaway from the substrate 110) and the central area A may have a crosssection surface with a flat shape or a straight-line shape (and withoutany curvature or any substantial curvature). The central area A may beparallel to a surface of the substrate 110.

A surface having a curvature may have better durability than a flatsurface against deformation due to external force. Therefore, the edgearea B may have a positive curvature that upwardly projects from thesubstrate 110 (or projects away from the substrate 110). The edge area Bof the encapsulation unit 360 may have a concave down shape (withrespect to the substrate 110) such as shown in FIGS. 4A-4C.

The encapsulation unit 360 may include an upper surface 360 a and alower surface 360 b at the first region X. The lower surface 360 b maybe a surface that faces the substrate 110, and the upper surface 360 amay be a surface that faces away from the substrate 110. Both the uppersurface 360 a and the lower surface 360 b at the edge area B may have apositive curvature such as shown in FIG. 4A. The upper surface 360 a andthe lower surface 360 b may both have a same shape (i.e., a curvedshape) such as shown in FIG. 4A.

Further, the upper surface 360 a and the lower surface 360 b at thecentral area A may have a flat shape or a straight-line shape such asshown in FIGS. 4A-4C. That is, the upper surface 360 a and the lowersurface 360 b at the central area A may both have a same shape such asshown in FIGS. 4A-4C.

The upper surface 360 a at the first region X may have a flat shape thatis parallel to the substrate 110 (regardless of the lower surface 360 b)such as shown in FIGS. 4A-4C.

The encapsulation unit 360 may also include an upper surface 360 c and alower surface 360 d at the second region Y. The lower surface 360 d maybe a surface that faces the substrate 110, and the upper surface 360 cmay be a surface that faces away from the substrate 110. The uppersurface 360 a at the first region X and the upper surface 360 c at thesecond region Y may both be separately flat and parallel to thesubstrate 110 such as shown in FIGS. 4B-4C. The upper surface 360 a ofthe encapsulation unit 360 at the first region X and the upper surface360 c of the encapsulation unit 360 at the second region Y may be formedalong a common plane such as shown in FIG. 4C.

A height d may be a distance between a first plane defined by the lowersurface 360 d of the encapsulation unit 360 at the second region Y and asecond plane (parallel to the first plane) defined by a top point of thelower surface 360 b of the encapsulation unit 360 at the first region X.The top point may be a point of the lower surface 360 b that is furthestfrom the substrate 110 (or the light emitting unit 120). The height dmay range from 10 μm to 100 μm. If the height d is 10 μm or more,degradation of picture quality caused by an interference phenomenonbetween light emitted from the light emitting device 300 to theencapsulation unit 360 and light incident to the encapsulation unit 360from outside may be reduced. If the height d is 00 μm or less, thicknessof the device may be prevented from becoming too thick.

Stated differently, the encapsulation unit 360 may include a firstsurface (i.e., the lower surface 360 b) at the first region X that facesthe substrate 110 and a second surface (i.e., the lower surface 360 d)at the second region Y that faces the substrate 110, where the firstsurface includes a top point that is furthest from the substrate 110.The second surface may define a first plane and the top point may be ona second plane that is parallel to the first plane. A distance betweenthe first plane and the second plane may be within a range of 10 μm to100 μm.

As described above, an encapsulation unit of a first region or a part ofan encapsulation unit may have a curvature. However, the encapsulationunit is not limited to the above shape. The light emitting device mayalso have two or more curvatures.

The light emitting unit 120, as discussed above, may include a pluralityof unit pixels with each unit pixel including a plurality of subpixels.For example, FIGS. 1A-1C show different arrangements of red, blue, greenand white light emitting layers to produce various combinations of red,blue and green light. Other combinations and/or colors may be used. Thelight emitting layers of the subpixels may include phosphorescencematerial and/or fluorescence material. The arrangements of FIGS. 1A-1Cmay be provided within any of the embodiments of the present inventionand/or displays associated with each of FIGS. 2A-4C.

In a case where the subpixel emits red light, the emitting layer of thesubpixel may include a host material including carbazole biphenyl (CBP)or 1,3-bis(carbazol-9-yl (mCP), and may be formed of a phosphorescencematerial including a dopant material including PQIr(acac)(bis(1-phenylisoquinoline)acetylacetonate iridium),PQIr(acac)(bis(1-phenylquinoline)acetylacetonate iridium),PQIr(tris(1-phenylquinoline)iridium), or PtOEP(octaethylporphyrinplatinum) or a fluorescence material including PBD:Eu(DBM)3(Phen) orPerylene.

In the case where the subpixel emits green light, the emitting layer mayinclude a host material including CBP or mCP, and may be formed of aphosphorescence material including a dopant material includingIr(ppy)3(fac tris(2-phenylpyridine)iridium) or a fluorescence materialincluding Alq3(tris(8-hydroxyquinolino)aluminum).

In the case where the subpixel emits blue light, the emitting layer mayincludes a host material including CBP or mCP, and may be formed of aphosphorescence material including a dopant material including(4,6-F2ppy)2Irpic or a fluorescence material including spiro-DPVBi,spiro-6P, distyryl-benzene (DSB), distyryl-arylene (DSA), PFO-basedpolymers, PPV-based polymers, or a combination thereof.

And a difference between driving voltages, e.g., the power voltages VDDand Vss of the light emitting device may change depending on the size ofthe light emitting device 100 (or 200 or 300) and a driving manner. Amagnitude of the driving voltage is shown in the following Tables 1 and2. Table 1 indicates a driving voltage magnitude in case of a digitaldriving manner, and Table 2 indicates a driving voltage magnitude incase of an analog driving manner.

TABLE 1 Size (S) of display panel VDD-Vss (R) VDD-Vss (G) VDD-Vss (B) S< 3 inches 3.5-10 (V) 3.5-10 (V) 3.5-12 (V) 3 inches < S < 20 inches  5-15 (V)   5-15 (V)   5-20 (V) 20 inches < S   5-20 (V)   5-20 (V)  5-25 (V)

TABLE 2 Size (S) of display panel VDD-Vss (R, G, B) S < 3 inches 4~20(V) 3 inches < S < 20 inches 5~25 (V) 20 inches < S 5~30 (V)

Any reference in this specification to “one embodiment,” “anembodiment,” “example embodiment,” etc., means that a particularfeature, structure, or characteristic described in connection with theembodiment is included in at least one embodiment of the invention. Theappearances of such phrases in various places in the specification arenot necessarily all referring to the same embodiment. Further, when aparticular feature, structure, or characteristic is described inconnection with any embodiment, it is submitted that it is within thepurview of one skilled in the art to effect such feature, structure, orcharacteristic in connection with other ones of the embodiments.

Although embodiments have been described with reference to a number ofillustrative embodiments thereof, it should be understood that numerousother modifications and embodiments can be devised by those skilled inthe art that will fall within the spirit and scope of the principles ofthis disclosure. More particularly, various variations and modificationsare possible in the component parts and/or arrangements of the subjectcombination arrangement within the scope of the disclosure, the drawingsand the appended claims. In addition to variations and modifications inthe component parts and/or arrangements, alternative uses will also beapparent to those skilled in the art.

What is claimed is:
 1. A light emitting device comprising: a substrate;a light emitting unit on the substrate; and an encapsulation unit havinga first region corresponding to the light emitting unit and a secondregion outside of the first region to couple with the substrate via asealant, the first region including a central area and an edge areaabout the central area, wherein the central area of the first region hasa flat shape and the edge area of the first region has a positivecurvature that projects away from the substrate, wherein the secondregion is coupled at a periphery of the substrate, and a height betweena first plane defined by a lower surface of the encapsulation unit atthe second region and a second plane defined by a lower surface of theencapsulation unit at the central area is 10 μm to 100 μm, wherein thefirst region and the second region have a same thickness.
 2. The lightemitting device of claim 1, wherein a lower surface of the encapsulationunit at the central area has the flat shape and a lower surface of theencapsulation unit at the edge area has the positive curvature.
 3. Thelight emitting device of claim 2, wherein the lower surface of theencapsulation unit at the central area is parallel to a surface of thesubstrate.
 4. The light emitting device of claim 1, wherein an uppersurface of the encapsulation unit at the central area has the flat shapeand an upper surface of the encapsulation unit at the edge area has thecurvature.
 5. The light emitting device of claim 4, wherein the uppersurface of the encapsulation unit at the central area is parallel to asurface of the substrate.
 6. The light emitting device of claim 1,wherein a lower surface of the encapsulation unit at the central areahas the flat shape and a lower surface of the encapsulation unit at theedge area has the positive curvature, and an upper surface of theencapsulation unit at the central area has the flat shape and an uppersurface of the encapsulation unit at the edge area has the positivecurvature.
 7. The light emitting device of claim 6, wherein the lowerand upper surfaces of the encapsulation unit at the central area areparallel to a surface of the substrate.
 8. The light emitting device ofclaim 1, further comprising a thin film transistor including asemiconductor layer, a gate electrode, a source electrode and a drainelectrode on the substrate.
 9. The light emitting device of claim 1,wherein the encapsulation unit comprises glass, plastic or metal. 10.The light emitting device of claim 1, wherein the light emitting unitincludes a plurality of sub pixels, each of the sub pixels comprises afirst electrode, a light emitting layer and a second electrode providedon the first electrode, and at least one of the plurality of sub pixelsincludes a phosphorescence material.
 11. The light emitting device ofclaim 1, further comprising a getter provided between the first regionof the encapsulation unit and the light emitting unit.
 12. A lightemitting device comprising: a substrate; a light emitting unit on thesubstrate; and an encapsulation unit having a first region correspondingto the light emitting unit and a second region outside of the firstregion to couple with the substrate via a sealant, the first regionincluding a central area and an edge area about the central area,wherein a lower surface of the encapsulation unit at the central areahas a flat shape and a lower surface of the encapsulation unit at theedge area has a positive curvature that projects away from thesubstrate, wherein the second region is coupled at a periphery of thesubstrate, and a height between a first plane defined by a lower surfaceof the encapsulation unit at the second region and a second planedefined by the lower surface of the encapsulation unit at the centralarea is 10 μm to 100 μm, wherein an upper surface of the encapsulationunit at the first region has a flat shape.
 13. The light emitting deviceof claim 12, wherein the upper surface of the encapsulation unit at thefirst region and an upper surface of the encapsulation unit at thesecond region are parallel to a surface of the substrate.
 14. The lightemitting device of claim 13, wherein the upper surfaces of theencapsulation unit at the first and second regions are on a same plane.15. The light emitting device of claim 13, wherein the upper surfaces ofthe encapsulation unit at the first and second regions are on differentplanes.
 16. The light emitting device of claim 12, wherein the lowersurface of the encapsulation unit at the central area is parallel to asurface of the substrate.
 17. The light emitting device of claim 12,further comprising a thin film transistor including a semiconductorlayer, a gate electrode, a source electrode and a drain electrode on thesubstrate.
 18. The light emitting device of claim 12, wherein theencapsulation unit comprises glass, plastic or metal.
 19. The lightemitting device of claim 12, wherein the light emitting unit includes aplurality of sub pixels, each of the sub pixels comprises a firstelectrode, a light emitting layer and a second electrode provided on thefirst electrode, and at least one of the plurality of sub pixelsincludes a phosphorescence material.
 20. The light emitting device ofclaim 12, further comprising a getter provided between the first regionof the encapsulation unit and the light emitting unit.